As electronics evolve, there is an increased need for miniature switches that are provided on semiconductor substrates along with other semiconductor components to form various types of circuits. These miniature switches often act as relays, generally range in size from a micrometer to a millimeter, and are generally referred to as microelectromechanical system (MEMS) switches.
In some applications, MEMS switches are configured as switches and replace field effect transistors (FETs). Such MEMS switches reduce insertion losses due to added resistance, and reduce parasitic capacitance and inductance inherent in providing FET switches in a signal path. MEMS switches are currently being deployed in many radio frequency (RF) applications, such as antenna switches, load switches, transmit/receive switches, tuning switches, and the like. For instance, transmit/receive systems requiring complex RF switching capabilities may utilize a MEMS switch.
For such applications, MEMS switches are subjected to a large number of open and close contact cycles where switch contacts are actuated between an open position where corresponding contacts are spaced apart and a closed position where corresponding contacts are in contact with each other. As the open and close contact cycles are repeated, maintaining a low overall contact resistance for the MEMS switches can be challenging for a number of reasons. For example, residual manufacturing contaminants may be present on one or both of the corresponding contacts that can contribute to reduced contact area during repeated open and close cycles, thereby increasing contact resistance. In a similar manner, material transfer between the corresponding contacts after repeated open and close cycles can contribute to an increased contact resistance. Additionally, MEMS switches may be subjected to hot switching events that can exacerbate the problems associated with contaminants and/or material transfer. During switching cycles, a difference in potential may be present across corresponding contacts during the periods in which the corresponding contacts approach each other, touch, and separate from one another. When the distance between the corresponding contacts is small, electric fields can enable field emission of electrons and eventually breakdown and arcing between the corresponding contacts. This can lead to significant material transfer between the corresponding contacts, which in turn can reduce contact force and/or contact area, thereby increasing contact resistance. Additionally, this can lead to pyrolysis, or thermal decomposition, at contact surfaces which can create non-conductive and load bearing films.
The art continues to seek improved MEMS switches that provide desirable performance characteristics over multiple open and close cycles while being capable of overcoming challenges associated with conventional MEMS switches.